In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit or MEMs device. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon.
In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (i.e., such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing components of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. An etching gas is then flowed into the chamber and energized to form a plasma to etch exposed areas of the substrate.
Referring now to FIG. 1, a simplified diagram of an inductively coupled plasma processing apparatus 200 includes a plasma chamber (chamber) 202 having a bottom chamber section 250 forming a sidewall of the chamber, an upper chamber section 244 also forming a sidewall of the chamber, and a cover 252. Process gas is flowed into chamber 202 from gas distribution system 222. The process gas may be subsequently ionized to form a plasma 260, in order to process (e.g., etching or deposition) exposed areas of substrate 224, such as a semiconductor substrate or a glass pane, supported on an electrostatic chuck (chuck) 216 with an edge ring 215 around the outer periphery of the chuck 216. Details of an exemplary gas distribution system may be found in commonly-owned U.S. Pat. No. 8,088,248, the disclosure of which is hereby incorporated by reference. Plasma processing gases commonly used include C4F8, C4F6, CHF3, CH2F3, CF4, HBr, CH3F, C2F4, N2, O2, Ar, Xe, He, H2, NH3, SF6, BCl3, and Cl2.
Induction coil 231 is separated from the interior of the plasma chamber by a dielectric window 204 forming the upper wall of the chamber, and generally induces a time-varying electric current in the plasma processing gases to create plasma 260. The window both protects induction coil from plasma 260, and allows the generated RF field 208 to generate an inductive current 211 within the plasma processing chamber. Further coupled to induction coil 231 is matching network 232 coupled to RF generator 234. The RF generator 234 supplies RF current preferably at a range of about 100 kHz-100 MHz, and more preferably at 13.56 MHz. Matching network 232 attempts to match the impedance of RF generator 234 to that of the plasma 260 (typically operating at about 13.56 MHz and about 50 ohms). Additionally, a second RF energy source 238 may also be coupled through matching network 236 to the bottom electrode 216 in order to apply an RF bias to the substrate 224 (e.g., 2 MHz). Gases and byproducts are removed from the chamber by a vacuum pump 220.
Generally, some type of cooling system 240 is coupled to chuck 216 in order to maintain the substrate 224 at a desired temperature. The cooling system itself is usually comprised of a chiller that pumps a coolant through cavities within the chuck, and helium gas is pumped between the chuck and the substrate to control thermal conductance between the substrate and the chuck. Increasing helium pressure increases the heat transfer rate and decreasing helium pressure reduces heat transfer. Most plasma processing systems are also controlled by sophisticated computers comprising operating software programs. In a typical operating environment, manufacturing process parameters (e.g., voltage, gas flow mix, gas flow rate, pressure, etc.) are generally configured for a particular plasma processing system and a specific processing recipe.
In addition, a heating apparatus 246 may operate to control the temperature of the upper chamber section 244 of the plasma processing apparatus 200 such that the inner surface of the upper chamber section 244, which is exposed to the plasma during operation, is maintained at a controlled temperature.
The upper chamber section 244 can be a machined piece of aluminum or hard anodized aluminum which can be removed for cleaning or replacement thereof. The inner surface of the upper chamber section is preferably anodized aluminum or a plasma resistant material such as a thermally sprayed yttria coating.
The volume of material in the upper chamber section tends to add a substantial thermal mass to the plasma processing system. Thermal mass refers to materials that have the capacity to store thermal energy for extended periods. In general, plasma processes tend to be very sensitive to temperature variation. For example, a temperature variation outside the established process recipe can directly affect the etch rate. Temperature repeatability between substrates is often desired, since many plasma processing recipes must be performed as multi-step processes at different temperatures which must be maintained within tight tolerances. Because of this, the upper chamber section is often temperature controlled in order to achieve target temperature settings.
Upper chamber section design also mitigates temperature variation in the plasma processing system. A replaceable upper chamber to reduce temperature variation employing a thermal choke, minimizing heat transfer, and a thermal mass, providing azimuthal temperature uniformity, in the upper chamber section is disclosed in commonly-owned U.S. Patent Publication No. 2011/0056626, the disclosure of which is hereby incorporated by reference.
Temperature variation control in the dielectric window of the upper chamber section would be desirable. Dielectric windows can develop non-uniform temperature gradients during processing. An upper surface to lower surface temperature gradient of the dielectric window can result from cooling the outer surface of the dielectric window by forced air or liquid and heating of the inner surface due to process conditions inside the chamber. Additionally, a center to edge temperature gradient can result from heat loss at the edge of the dielectric window to the atmosphere and thermal contact area with the chamber.